Removal of naphthalene constituents from gases



sept. 24, 1929. E. H. BIRD 1,729,562

REMOVAL OF NAPHTHALENE CONSTITUENTS FROM GASES Filed Feb. 15, 1925 l A MMM Patented Sept. 24, 1929 UNITED STATES PATENT OFFICE EUGENE H. BIRD, OF PITTSBURGH, PENNSYLVANIA, ASASIGNOR TO THE KOPPERS ('.}0MPA1\`I'Y, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA REMOVAL F NAPHTHALENE CONSTITUENTS FROM GASES Application field February 13, 1923.

This invention relates essentially to the removal of naphthalene and analogous hydrocarbons from coal gas, Water gas, coke oven gas, or other gases employed for heat- 6 ing or illuminating purposes. The process is preferably applied after the gas has been subjected to the usual treatment of cooling and condensation and the removal of tar and ammonia. Although the invention is here- 10 inai'ter described as applied tothe removal of naphthalene, Which is one of the most important applications of the invention, the invention is not limited in scope to this application, being of general utility for the removal from the gas of other hydrocarbons,

such as are characterized by having a relatively small vapor tension and by being present in vapor form in gas at ordinary ranges of temperature, in relatively small- Z0 amounts, and near their saturation limit. Antliracene is an example of such other high hydrocarbons, the removal of Which may be ettected by the present invention.

N aphthalene is formed in connection with the production of most types of fuel or illuminating gases. It is a solid at ordinary temperatures and pressures and has a melting point of approximately 80O C. It, however, exists in a state of vapor dilfused through the gas at temperatures far below its melting point and of course has at each temperature a definite saturation limit. For example, 100 cu. ft. of dry gas saturated 5 with naphthalene at 25 C. contain 25.5 grains of naphthalene. At o C. the same volume of saturated gas carries 15.5 grains, and at 15 C. the saturation limit is 9.4: grains of naphthalene. -When gas saturated with :0 naphthalene at any temperature below its melting point. is cooled, the vapor passes directly into the solid state in the form of very light flaky flat crystals which occupy a large volume in proportion to their weight.

5 This property renders the naphthalene eX- tremely troublesome to the gas manufacturer and to the consumer. Although the Weight of the naphthalene that may be actually deposited from a given quantity o 9 gas may be small, the crystals occupy so large Serial No. 618,838.

a space as to obstruct the distributing mains and service apparatus.

Naphthalene Which has once been deposited Will pass from the solid state directly into that of vapor as soon as it is slightly warmed or brought into contact with a gas carrying less naphthalene than theY saturation limit and thus naphthalene that has been deposited in the pipes in quantities too small to cause trouble may evaporate again and pass off With further amounts of gas When this reaches the deposit in an unsaturated condition. This same naphthalene may be redeposited farther along in the system if the gas becomes suiiciently cool and so serious local stoppages may occur although the system as a Whole may contain very little naphthalene.

Under present conditions of gas manufacture, naphthalene troubles have become more numerous and more acute than formerly because in present practice the tendency is to produce what is technically known as a dry gas, i. e. a gas containing little or no readily condensible oils. It the gas contains a sufficient amount ot1 such oils as it commonly did in former practice, these would condense along with the naphthalene and prevent the latter from goingr into the flaky crystalline Condition. In fact the amount of oils so condensed would, in most cases, be sufficient to keep the naphthalene in solution so that it would eventually find its Way to the drains and drips and be pumped out of the system. In present practice, however, the gas seldom contains sucient oils to prevent naphthalene stoppages and trouble may occur even when the gas leaving the Works contains as little as 5 or 6 grains of naphthalene per 100 cu. ft.

It is very desirable, therefore, to treat the gas at the point of manufacture in such a Way that it will be practically free from naphthalene. A considerable amount ot the naphthalene may be removed by thoroughly cooling the gas, by the aid of Water either in indirect coolers or in scrubbing apparatus in which the Wat-er is brought directly into contact with the However, the best that has been accomplished by the cooling proc-` lili) ess is to remove such amounts of naphthalene as occur beyond the' saturation limit determined by the temperature of the water, so that the gas after the cooling treatment inmost cases still contains enough naphthalene to cause trouble.

Methods that have so far been attempted for the removal of the small amounts of naphthalene that remain, even after cooling the gas as much as possible, have been based on the fact that naphthalene is soluble in oils, such as anthracene oil, creosote oil and various petroleum oils. Two principal dlfliculties have been encountered in this connection. The first arises from'the fact that very small amounts of naphthalene have to be dealt with and these small amounts are distributed through very large volumes of gas and there has heretofore been considerable diiiculty in securing a distribution of the oil through the large gas volume adequate to reach the naphthalene ei'ectively without using excessive quantities of oil. Creosote oil, for example, will readily take up 5% ot its weight in naphthalene. In ordinary cases, we have about' 10 to 15 grains of naphthalene to be removed per 100 cu. ft. of gas tlat in a plan producing 1,000,000 cu.

o oil per day should be sufiicient for the removal of the naphthalene. Some gasworks have experimented with mechanical scrubbers for the application of oil to the gas, but these have the'disadvanta es of causing the gas to'lose its pressure, o mechanical troubles, and of requiring considerable attention with heavy labor expense. A second diiiiculty in connection with the present attem ts to apply oil for na hthalene removal is t at if large amounts o oil are used, they absorb considerable amounts of benzols, thus lowering the heating value of the gas. In dealing with domestic as in most cases under normal conditions t e value of the benzols in the gas is greater than their value recovered from the oil.

This invention provides an effective process for bringing, small amounts of oil in contact with large volumes'of gas for the substantially complete removal of the naphthalene. By the invention, the absorption of beniol or other enriching hydrocarbon from the gas is eliminated, or reduced to such a mereA trace as to be of no practical consequence whatever. Moreover, expensive ""installations are eliminated, there is p'racti,`

cally no loss of gas pressure, tus is simple, inexpensive, tle if any attention.

`In addition to the general objects recited above, the invention has for further objects such other improvements or advantages in operation and results as are found to obtain and the apparaand requires lit- 1n the process or apparatus hereinafter described or claimed.

gas per day from 40 to 60 gallons of In the accompanying rawingl forming a part of this specificationandA s owing, for purposes of exemplilication, a preferred form and manner in which the invention may be embodied and practiced, but without limiting the claimed invention to such illustrative instance, the figure shows a `diagrammatic representation of apparatus for carrying out the process of the invention.

According to the invention, the gas is passed through a bedofabsorbent solid material, such as wood shavings coke breeze or other suitable material offering relatively large surfaces and capable of holding a considerable amount or' liquid by adhesion. The naphthalene-solvent, or carrier liquid may be pumped intermittently over this bed at such intervals and rates as to insure proper distribution throughout the bed, as to bring about an intimate contact between relatively large volumes of amount of liquid. Referring to the drawing, A represents a purifier box, for example, of the type commonly employed in the iron oxide process for removing hydrogen sulphide from gas. The box'is lilled with a bed B of absorbent solid material having characteristics mentioned above. A satisfactory material for this purpose is coke breeze. The bed of absorbent material is supported on the grid C located above the bottomA of the uriiier box. `It is preferable to employ a re atively wide and shallow bed so that the pressure drop of the gas will be relatively small. The gas is passed from the inlet K continuously underneath the grid and rising through the bed, passes out of the top of the box, through the outlet L. The absorbent liquid, such as oil, is pumped from the tank D through pump E, and the line F, to the sprays G, where it is distributed over the bed. This pumping is conducted at such a rate as to insure adequate distribution of theoil through the bed. The amount of oil used depends upon the quality of the oil and the amount of naphthalene in the gas. Where employing a petroleum oil such as gas oil, the amount of oil used is greater than with creosote or anthracene oil ordinarily employed, but there is an advantage in using the petroleum oil because of the com arative ease of distributing the relai tive y largeamounts and because used oil need not be regenerated but may be disposed of by mixing it with the coal in the case of a coal gas plant or by using it in the carburetors inthe case of a water gas plant.

en using gas oil there may for example be employed 100 to 200 gallons for substantially complete removal of the naphthalene. This amount of oil will remove only insignificant amounts of benzol and the consequent reduction of Aheating value is less than 1 B. t. u. per cu'. ft. of gas. The oil need be l pumped only at comparatively long inter gas and therelatively small' vals, e. g. once every eight hours; but the rate of pumping should be rapid sol as to eect good distribution. The pumping may be started and stopped automatically by a clockwork arrangement operating in conjunction with the pump E. The used oil drains from the bottom of the box through the sealed pipe H, into the tank I, from which it may be disposed of as above described or it may be regenerated if desired by removing the naphthalene by heating, aeration or steaming, or by a combination of any of these methods.

The term naphthalene constituents employed in the claims is not limited to naphthalene, but includes analogous hydrocarbons for example, anthracene, having the naphthalene characteristics hereinbefore mentioned.

The invention as hereinabove set forth may be variousl embodied within the scope of the claims ereinafter made.

I claim:

1. A continuous process for removing certain constituents from gases, which comprises: continuously passing the gas through a bed of solid material drenched with a liquid for removing said certain constituents froml the gas; discharging spent liquid containing the said constituents from said bed during gas flow therethrough; and supplying said liquid to said bed during such continuous gas treatment by intermittently drenching the bed with the liquid at long intervals for a. shorter period of time than such interval and at a high rate of speed, and so delivering at each of such intermittent drenchings substantially such volume 0f liquid as to effect distribution throughout the bed and bring about an intimate contact between relatively large volumes of gas and the relatively small amount of liquid.

2. A continuous process for removing naphthalene constituents from fuel gases, which comprises: continuously passing the gas through a bed of non-reacting solid material drenche`d with a naphthalene absorbent liquid; discharging` absorbent liquid containing the naphthalene from the bed of non-reacting material during gas flow therethrough; and supplying the absorbent liquid to said bed during such continuous gas-treatment by intermittently drenching the bed with the liquid at long intervals for a shorter period of time and at a high rate of speed.

3. A method for distributing liquid over a bed of solid material for effecting contact of gas passing through said bed with liquid therein, which comprises: passing gas through a bed of solid material treated with a liquid for contact with the gas; discharging spent liquid from said material; and supplying said liquid to said bedby intermittently delivering at long intervals substantially the entire volume of liquid required ta -high rate of speed and for a. shorter period m hand.

y EUGENE H. BIRD.

be delivered for a next interval and at a 

